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Results and Discussion Distribution and Abundance River-wide catch rates were fairly high in all four rivers during 1994 compared with most years of ISMP data (Figures 9, 10, 11, 12; Table B-1). Mean CPE declined slightly in the Yampa River, but river-wide catch rates were higher than 1993 in the Green, Colorado, and White rivers. In general, riverwide catch rates in all four rivers have been relatively consistent over the last few years. Catch rates are higher than early in ISMP. The sustained high catch rates in all four rivers suggest more subadult and adult Colorado squawfish in the upper basin than when the monitoring program began. Size Distribution The size distribution in the Green and Colorado rivers continues to reflect a large group of fish that were produced in 1986 or 1987 (Figure 13; Table B-2, B-3). Many of these fish have reached adult size. Using 5-cm length groups, the highest percentage of fish collected in the Green and Colorado rivers were between 45 and 50 cm long (compared with 35 to 40 cm in 1993). The median length of all fish collected from both rivers has been steadily increasing as the cohort mentioned above has been growing in length and preparing to enter the adult population (Figures B-1, B-2). Size distributions of Colorado squawfish from both rivers also indicate a substantial number of smaller fish as well. Some of these smaller fish (± 300 mm) have been captured in the upper Green River (reaches 2 and 3) in recent years. Most fish collected from the Yampa and White rivers are adults, but both rivers also contain a high percentage of subadult and young adult-size fish. Size distributions and median length of fish collected from these two rivers have been relatively constant since ISMP began (Figures B-3, B-4). This constant size distribution suggests slow, but regular recruitment into the adult populations of the two rivers and the entire upper basin. Sym atp ric Species Native Species-Razorback sucker Xyrauchen texanus was only collected from Reach 2 in the Green River (Table B~). Five individuals were captured there, compared with two individuals in 1992 and three in 1991 and 1993. Twelve or more razorbacks were collected from the Green River during ISMP sampling from 1986-1990 (McAda et al. 1994a). One humpback chub was collected from the Green River and another was collected from the Colorado River. It is important to note that these species are collected incidentally to sampling for Colorado squawfish. This portion of ISMP is not designed as population monitoring for either of these two species. Introduced Species-Northern pike Esox Lucius continued to be observed in relatively high numbers in the Yampa and upper Green Rivers (Table B-4). A total of 39 northern pike were observed in the upper Green and 49 were observed in the Yampa River. These numbers compare with 23 in the Green and 29 in the Yampa during 1993. Seventeen smallmouth bass Micropterus dolomieui were collected from the Green River and 20 were collected from the Yampa River (Table B-4). One smallmouth and three largemouth bass were caught in the Colorado River. 11